Between 1999 and 2007, several successive years of severe drought put South East Queensland's water supply under immense pressure. The decision was taken in 2005 to build a seawater desalination plant and three water recycling advanced treatment plants as part of a large investment plan to secure the region's potable water supply. The infrastructure built and commissioned in the past 3 years has a combined capacity producing more than 350,000 m3 per day of very high quality water that can be used either directly (seawater desalination) or indirectly (recycled water) for supplying drinking water. All the plants primarily rely on reverse osmosis membranes for water purification which is an effective and reliable barrier to contaminants, but also requires high energy consumption and a high level of pre-treatment and chemicals. In this paper, the actual energy consumption of two of the plants (the seawater desalination plant and one water recycling plant) was investigated with the perspective of drinking water production over the July 2009–June 2010 period. Eolia™ Potable Water, a Life Cycle Analysis tool developed by Veolia Environnement Research & Innovation, was used to model the processes and estimate the greenhouse gases (GHG) emissions from both plants. As expected, the energy requirement of the desalination was higher (approximately 2.2 times) than the water recycling plant. The plants were found to be significantly more energy efficient when operated at higher flow. In both cases, the purchase of electrical energy represented by far the major contribution to GHG emissions. Indirect GHG emissions from chemical consumption could be reduced at the water recycling plant by optimising the dose of ferric chloride used at the plant and sourcing the chemical from a less distant supplier.